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An improved model for the French genetic evaluation of dairy bulls on length of productive life of their daughters

Published online by Cambridge University Press:  09 March 2007

V. Ducrocq
V. Ducrocq*
Affiliation:
Station de Génétique Quantitative et Appliquée, Département de Génétique Animale, Institut National de la Recherche Agronomique, 78352 Jouy en Josas, France
*
†E-mail: ducrocq@dga.jouy.inra.fr
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Abstract

Functional longevity of dairy cows has been routinely evaluated in France since 1997 using a survival analysis model. Recently, we proposed a genetic trend validation test that could be used before including national data in an international evaluation of bulls on longevity of their daughters. Its application to the French Holstein data revealed a large overestimation of the genetic trend. It was found that the bias is the result of a change in the baseline hazard rate over time. A new proportional hazards model is proposed which accounts for this change. In the new model, the baseline is described as a stratified, piecewise Weibull hazard function within lactation, i.e. a function of the number of days since the most recent calving. Stratification is within year and parity. Different Weibull hazard functions are used over four periods: 0 to 270 days, 271 to 380 days, 381 days to day when dried, dry period until the next calving. The non-genetic effects included in the model were slightly different from the previous one. In particular the interaction effects between the within herd-year class of production and lactation number × stage of lactation on the one hand and year-season were accounted for. The estimated genetic variance was smaller than with the old model. The new genetic trend is almost flat. An illustration of the efficiency of selection on the estimated breeding values for longevity is presented.

Keywords

dairy cattlegenetic analysislongevitysire evaluationsurvival
Type
Research Article
Information
Animal Science , Volume 80 , Issue 3 , June 2005 , pp. 249 - 256
Copyright
Copyright © British Society of Animal Science 2005

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